I just checked the Global Riing card on Telestial. They cite a cost of $0.52 per minute for calls from most countries but the card is sold for a cost of $69 and only has $20 of airtime. So for that initial use you are actually paying a bit over 3 times the stated rate per minute or about $1.70 per minute. That isnt a deal. As you add usage the cost per minute goes down.